Confirmed the behaviour. In addition, when you do:
/aline 4 @window column1 $chr(9) column2 $chr(9) column3 etc
... while in prior mIRC's, any column not containing colour codes reverted to the red-4 colour.
Column 2 did inherit the red-4 colour by adding a ctrl-K to the end of column 1, but that requires fixing some fline search-strings, etc.
The new /aline -t switch isn't mentioned in the /help file